(patch) reduce confusion with absolute pathnames in vnconfig

[lawgiver]

Hello, this is my first patch.

vnconfig(8) should print absolute pathnames of configured disk images,
instead of repeating whatever was given to -c.

Contrived example:

$ doas vnconfig -l
vnd0: covering ../images/../images/foo on sd4l, inode 15301672
vnd1: covering foo on sd4l, inode 15562887
vnd2: covering foo on sd4l, inode 15562888

With this patch:

$ doas vnconfig -l           
vnd0: covering /home/user/images/foo on sd4l, inode 15301672
vnd1: covering /home/user/images/a/foo on sd4l, inode 15562887
vnd2: covering /home/user/images/b/foo on sd4l, inode 15562888

Index: mount_vnd.c
===================================================================
RCS file: /cvs/src/sbin/mount_vnd/mount_vnd.c,v
retrieving revision 1.20
diff -u -p -r1.20 mount_vnd.c
--- mount_vnd.c 24 Jan 2016 06:32:33 -0000      1.20
+++ mount_vnd.c 16 Sep 2018 06:05:02 -0000
@@ -143,6 +143,7 @@ main(int argc, char **argv)
 
        if (action == VND_CONFIG && argc == 2) {
                int ind_raw, ind_reg;
+               char realfile[PATH_MAX];
 
                if (opt_k || opt_K) {
                        fprintf(stderr,
@@ -167,7 +168,12 @@ main(int argc, char **argv)
                        ind_raw = 0;
                        ind_reg = 1;
                }
-               rv = config(argv[ind_raw], argv[ind_reg], action, dp, key,
+
+               if (realpath(argv[ind_reg], realfile) == NULL) {
+                       err(1, "invalid file path");
+               }
+       
+               rv = config(argv[ind_raw], realfile, action, dp, key,
                    keylen);
        } else if (action == VND_UNCONFIG && argc == 1)
                rv = config(argv[0], NULL, action, NULL, NULL, 0);